Erection problems? I'm a fairly overweight

I've got a slight query and I'd like some advice. I'm a fairly overweight guy and was quite badly obese until 22 (I'm now 25 and not as severe). I've been quite worried for awhile as I noticed that my penis has some trouble maintaining hardness. The mid section before the head and the head itself don't seem to have the problem, but the base does which loses some of my length and causes me to get soft when having sex. The base of my penis is partially reduced in visiibility due to a little bit of skin that covers some of it up friom when I was really obese and thus I've never really stimulated this area. During masturbation practice recently I found that stimulating that area causes a much greater erection but doesn't really sustain itself. Is there a way to resolve this problem? :/